1. Field of the Invention
The present invention relates to an optical module, an optical transceiver, a printed circuit board, and a flexible printed circuit board.
2. Description of the Related Art
An optical module includes optical high frequency components. A high frequency electrical signal is input to and/or output from the optical high frequency component. Therefore, the high frequency electrical signal input to the optical high frequency component, and the high frequency electrical signal output from the optical high frequency component propagate through a transmission line. At a connection position between the transmission lines, two circuit boards are connected to each other in an overlapping manner. Out of the two circuit boards, a circuit board located on a lower side is referred to as “first circuit board”, and a circuit board located on an upper side is referred to as “second circuit board”. For example, such a case that an optical high frequency component and a circuit board are connected to each other via a wiring circuit board is now considered. The circuit board such as a printed circuit board is the first circuit board, and the wiring circuit board such as a flexible printed circuit board is the second circuit board.
On the first circuit board, for example, a microstrip line is formed in order to transmit a high frequency electrical signal, and further, a first terminal part connected to one end part of the microstrip line is formed on a front surface of the first circuit board. On this occasion, the microstrip line is a transmission line for transmitting the high frequency electrical signal, and is formed in a manner that a ground conductor layer having a ground electrical potential is formed on a back surface of a dielectric layer, and a signal wire pattern having a line shape is formed on a front surface of the dielectric layer. Moreover, on the second circuit board, a second terminal part to be connected to the first terminal part is formed on a back surface of the second circuit board. Both the first terminal part and the second terminal part include a ground terminal and a signal terminal. The first terminal part and the second terminal part are physically in contact with (overlap) and connected to each other via a conductive bonding material such as solder. Note that, in Japanese Patent Application Laid-open No. 2009-94390, there is disclosed an optical module in which a flexible printed circuit is appropriately constructed so that a resonance frequency component of a circuit board for transmitting a high frequency is excluded from a used bandwidth.